1. Field of the Invention
The present invention relates to paging systems in general and in particular, to a paging controller used for encoding paging information into coded signals for transmission over a radio frequency link to a paging receiver.
2. Background Discussion
Paging receivers (pagers) are generally small, portable, battery-operated radio receivers designed to be carried on an individual. The communication technique used in paging systems is referred to as selective calling in which transmissions intended for a particular receiver will cause a response only in that receiver. Pager communication systems are well known in the art and operate with many types of coding schemes including single or multi-tone signals, selected combination of tone and voice signals, and digitally encoded signals. Typically, there are wide area paging communication systems capable of transmitting throughout a metropolitan area and local paging communication systems which transmit in a much smaller service area as, for example, a specific building complex or other facility. Wide area paging systems typically have a number of remote transmitting stations to cover a large area, while local paging systems typically have only one transmitting station. The range of operation of the various systems is generally determined by the power of the transmitter used.
To clearly understand the present invention, it is necessary to briefly explain the operation of a typical wide area paging communication system. FIG. 1 illustrates a typical wide area paging communication system 10 having a central controller 12 and a remote input/output (I/O) processor 14. System 10 is used for transmitting information from an originator to a person carrying a portable paging receiver 18 throughout a large metropolitan area. An example of such a paging system is a METRO-PAGE 200 terminal manufactured by Motorola, Inc. This paging system can handle up to 200,000 pagers having combinations of tone, voice, numeric, or alphanumeric paging.
In the operation of such a system, an originator 16 desiring to send information to a local paging receiver user, enters a pager identification number in an entry device and begins communication with the local I/O processor 14. The entry device, such as telephone 16, is used to access the data base in the central controller 12 to enter a paging receiver's identification number and messages intended therefor for subsequent transmission to the selected receiver. The telephone 16, is useful for entering voice or numeric data whereas a video display terminal, such as video display terminal 13, is useful for entering alphanumeric messages and for accessing and updating information in the central controller 12. A mass storage media, such as disk 20, provides a subscriber list of all the paging receiver ID's that are valid in the system 10. Filed under each pager ID in the subscriber list are several items that are needed by the central controller 12 to send or transmit a page including information, such as pager type, the particular pager address which corresponds to the pager ID, the maximum message storage time, how often delivery attempts are to be made, and additional statistical information useful in a feasible commercial operation of the system 10.
In a wide area paging system, it is cost effective to have a plurality of geographical remote transmission sites and to locate the telephone inputs (for local calls) and transmitter control units at the remote site in a single device referred to as the I/O processor 14. The I/O processor 14 substantially reduces toll charges between the central controller 12 and the remote areas. This reduction in line cost typically means the difference between cost effective paging service at the remote site and providing no paging service at all.
In a wide area paging service, with the I/O processor 14 remotely located from the central controller 12, page requests can be processed in a number of ways. First, a tone alert page can be initiated by telephone input 16, processed by the I/O processor 14 using information received over communication link 24 from central controller 12, and transmitted over a transmitter output unit 22. Second, a tone and numeric page can be initiated by telephone input 16, processed by the I/O processor 14 using information from the central controller 12, and transmitted over transmitter 22. Third, tone and voice pages can be initiated by telephone 16 and subsequently transmitted over transmitter 22. Finally, alphanumeric information entered through an entry device, such as video display terminal 13 can be transmitted via communication link 24 to input/output processor 14 to be transmitted via transmitter 22. Thus, the central controller 12 directs the action in the remote I/O processor 14 with the I/O processor 14 controlling the telephone input and transmitter output.
Heretofore, an I/O processor 14 of this type (such as one included in a METRO-PAGE 200) has consisted of a 15-slot card rack power supply, processor board 26, time division multiplexer (TDM) switchboard 28, and serial to parallel board 29. Remaining slots have been filled by a combination of telephone input boards 30, transmitter output boards 32, communication boards 34, synthesizer boards 36, and a supervisory tone board 38. The TDM switchboard has enabled the transfer of digitized voice and tone information among the specialized boards. The serial to parallel board 29 has permitted the exchange of information between an I/O processor bus 42 and a TDM bus 40.
The dual telephone input board 30 has been able to interface with up to two telephone inputs. The dual transmitter output board has the capability to interface with up to two independent transmitters. The communication board has provided data input from a communication modem or the like. The multifunctional dual synthesizer has provided support for the radio frequency of the dual transmitter output board.
The supervisory tone board has provided continuously-variable sloped delta modulation idle patterns and a dual tone multifrequency control tone required by the other boards to insure proper operation of the I/O processor 14. In addition to generating tones, another function of the supervisory tone board has been to continuously monitor the activity status of all tones and to provide an activity alarm interrupt at the system annunciator unit 39 if a tone fails. Basically, the supervisory tone board has been used to generate audio tones that are used for signalling the originator. For example, the supervisory tone board has been equipped with voice messages to lead the originator through the steps of making a call to a paging receiver user. The multifunctional dual synthesizer has been used to convert the paging receiver ID and page information into one of several signalling formats, such as GSC, 5/6 tone, POCSAG, etc.
Furthermore, to enable the transfer of digitized voice and tone information within the I/O processor 14, a time division multiplex (TDM) bus structure 40 has been utilized. The digitized audio or TDM bus 40 has provided serial digitized audio data between the various boards of the I/O processor 14. The transfer of serial data on the TDM bus is controlled by the TDM switchboard. To communicate effectively with each board, however, the processor 26 has required an additional processor bus 42 for data and to control the functions of the individual boards. The processor bus has been a parallel bus architecture for expediting the exchange of information. Basically, the processor bus 42 has provided data and control information from the processor to each individual board while digitized audio data in the form of voice and tone information has been transferred between the boards on the TDM bus. To effect the exchange between the serial TDM bus 40 and the parallel processor bus 42, a serial to parallel board 29 is used.
While such a configuration has worked well to provide transfer of a large amount of data between the boards, such a system has been very costly due to the amount of hardware necessary for each board to interface with the TDM bus and processor bus separately. It would thus be highly desirable and very cost effective to eliminate the dual bus structure of the I/O processor and reduce the number of the boards required to provide the functions of the I/O processor in operation. It should be appreciated that any hardware and software reduction in the I/O processor is a substantial factor in achieving marketability success and consumer acceptance of the present invention.